Memory devices are often provided as internal storage areas in electronic devices such as personal computers (PCs), digital cameras and cellular telephones. In general, memory devices contain an array of memory cells for storing data, and row and column decoder circuits coupled to the array of memory cells for accessing the array of memory cells in response to an external address.
One type of memory is a non-volatile memory known as FLASH memory. FLASH memory is a type of EEPROM (electrically-erasable programmable read-only memory) that can be erased and reprogrammed in blocks. Many modern personal computers (PCs) have their BIOS stored on a FLASH memory chip so that it can easily be updated if necessary. Such a BIOS is sometimes called a FLASH BIOS. FLASH memory is also popular in wireless electronic devices because it enables the manufacturer to support new communication protocols as they become standardized and to provide the ability to remotely upgrade the device for enhanced features. FLASH memory typically utilizes one of two basic architectures known as NOR FLASH and NAND FLASH. The designation is derived from the logic used to read the devices.
As with most types of memory, including FLASH memory, it is desirable to test and verify the memory device during the development phase of a device, as part of the manufacturing process of the device and finally by the end user of the memory device.
During the development phase of a memory device, development prototype devices are often made which have additional memory circuitry used to store test instructions and commands. This additional memory circuitry is often hard coded and therefore changing or updating the test instructions and commands can be time consuming and labor intensive. In addition, this additional circuitry can consume large amounts of real estate on a device and therefore must be removed for production versions of the chip.
During the production phase of a memory device, device testing can be tedious and time consuming because the process often requires a test operator utilizing some type of probing device to verify the operation of each memory device. This consumes time and resources which can add up to significant costs. Thus, having the capability of performing self test operations on a memory device would improve time to market, increase production rates and generally reduce the overall cost of memory devices.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for memory devices to perform self test operations.